Communication networks providing for bi-directional communication are well-known. An example of such a network, embodied in a CATV communication system, is provided in commonly assigned co-pending U.S. patent application Ser. No. 06/373,765, now U.S. Pat. No. 4,533,948, filed April 30, 1982, entitled "CATV Communication System", and incorporated herein by reference.
The pending application referred to discloses a mechanism by which access to CATV communication resources is controlled so that unauthorized users are denied access and authorized users are granted access. The CATV communication network includes an upstream communication path and a downstream communication path. A node originating a message (a source node), which can be located at any respective point in the CATV system, transmits a verification message, referred to as a frame verifier (FV) code, as part of an upstream message. The headend apparatus of the CATV system examines the frame verifier code and rebroadcasts the received upstream message in the downstream portion of the cable spectrum only if the frame verifier code indicates that the source node is an authorized user, thereby granting the user access to the CATV resources. Conversely, the headend apparatus does not rebroadcast the upstream message if the frame verifier code indicates that the source node is not an authorized user, thereby denying the user meaningful access to the CATV resources. Thus, system access control is centralized at the headend.
It would be advantageous to provide for decentralized control over access to a communication network. Such an arrangement would permit a simplified headend apparatus to be a simple digital data repeater which unconditionally rebroadcasts upstream received messages on a downstream channel. By decentralizing access control, the initial cost of a communication network can be substantially reduced since the headend is not required to contain the components for restricting access. Access control can be added to a communication network by the operator as desired after the system is up and running.
It would be further advantageous to provide a communication network which does not rely on the headend equipment for access control because the headend environment is often very harsh. For example, it is not uncommon to place the headend equipment at the top of a mountain. Such environments require the equipment to be ruggedized. It is therefore desirable to keep the amount and complexity of the equipment at such sites to a minimum.